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id="post-meta"><div class="meta-firstline"><span class="post-meta-date"><svg class="meta_icon post-meta-icon" style="width:30px;height:30px;position:relative;top:10px"><use xlink:href="#icon-rili"></use></svg><span class="post-meta-label">发表于 </span><time class="post-meta-date-created" datetime="2022-09-19T09:16:49.000Z" title="发表于 2022-09-19 17:16:49">2022-09-19</time><span class="post-meta-separator">|</span><svg class="meta_icon post-meta-icon" style="width:18px;height:18px;position:relative;top:5px"><use xlink:href="#icon-gengxin1"></use></svg><span class="post-meta-label">更新于</span><time class="post-meta-date-updated" datetime="2024-04-26T09:52:18.870Z" title="更新于 2024-04-26 17:52:18">2024-04-26</time></span><span class="post-meta-categories"><span class="post-meta-separator">|</span><svg class="meta_icon post-meta-icon" style="width:18px;height:18px;position:relative;top:5px"><use xlink:href="#icon-biaoqian"></use></svg><a class="post-meta-categories" href="/categories/%E4%B8%AD%E9%97%B4%E4%BB%B6/">中间件</a><i class="fas fa-angle-right post-meta-separator"></i><svg class="meta_icon post-meta-icon" style="width:18px;height:18px;position:relative;top:5px"><use xlink:href="#icon-biaoqian"></use></svg><a class="post-meta-categories" href="/categories/%E4%B8%AD%E9%97%B4%E4%BB%B6/MySQL/">MySQL</a></span></div><div class="meta-secondline"><span class="post-meta-separator">|</span><span class="post-meta-wordcount"><svg class="meta_icon post-meta-icon" style="width:25px;height:25px;position:relative;top:8px"><use xlink:href="#icon-charuword"></use></svg><span class="post-meta-label">字数总计:</span><span class="word-count">2302</span><span class="post-meta-separator">|</span><svg class="meta_icon post-meta-icon" style="width:20px;height:20px;position:relative;top:5px"><use xlink:href="#icon-shizhong"></use></svg><span class="post-meta-label">阅读时长:</span><span>8分钟</span></span><span class="post-meta-separator">|</span><span class="post-meta-pv-cv" id="" data-flag-title="第九-MySQL子查询"><svg class="meta_icon post-meta-icon" style="width:25px;height:25px;position:relative;top:5px"><use xlink:href="#icon-eye"></use></svg><span class="post-meta-label">阅读量:</span><span id="busuanzi_value_page_pv"><i class="fa-solid fa-spinner fa-spin"></i></span></span></div></div></div><section class="main-hero-waves-area waves-area"><svg class="waves-svg" xmlns="http://www.w3.org/2000/svg" xlink="http://www.w3.org/1999/xlink" viewBox="0 24 150 28" preserveAspectRatio="none" shape-rendering="auto"><defs><path id="gentle-wave" d="M -160 44 c 30 0 58 -18 88 -18 s 58 18 88 18 s 58 -18 88 -18 s 58 18 88 18 v 44 h -352 Z"></path></defs><g class="parallax"><use href="#gentle-wave" x="48" y="0"></use><use href="#gentle-wave" x="48" y="3"></use><use href="#gentle-wave" x="48" y="5"></use><use href="#gentle-wave" x="48" y="7"></use></g></svg></section></header><main class="layout" id="content-inner"><div id="post"><article class="post-content" id="article-container"><h1 id="第09章-子查询"><a href="#第09章-子查询" class="headerlink" title="第09章_子查询"></a>第09章_子查询</h1><p>子查询指一个查询语句嵌套在另一个查询语句内部的查询，这个特性从MySQL 4.1开始引入。</p>
<p>SQL 中子查询的使用大大增强了 SELECT 查询的能力，因为很多时候查询需要从结果集中获取数据，或者需要从同一个表中先计算得出一个数据结果，然后与这个数据结果（可能是某个标量，也可能是某个集合）进行比较。</p>
<h2 id="1-需求分析与问题解决"><a href="#1-需求分析与问题解决" class="headerlink" title="1. 需求分析与问题解决"></a>1. 需求分析与问题解决</h2><h3 id="1-1-实际问题"><a href="#1-1-实际问题" class="headerlink" title="1.1 实际问题"></a>1.1 实际问题</h3><p><img src= "" data-lazy-src="https://www.naste.top:9000/webp/1554991034688.webp" alt="1554991034688" style="zoom:80%;" /></p>
<p>现有解决方式：</p>
<figure class="highlight plaintext"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br></pre></td><td class="code"><pre><span class="line">#方式一：</span><br><span class="line">SELECT salary</span><br><span class="line">FROM employees</span><br><span class="line">WHERE last_name = &#x27;Abel&#x27;;</span><br><span class="line"></span><br><span class="line">SELECT last_name,salary</span><br><span class="line">FROM employees</span><br><span class="line">WHERE salary &gt; 11000;</span><br><span class="line"></span><br><span class="line">#方式二：自连接</span><br><span class="line">SELECT e2.last_name,e2.salary</span><br><span class="line">FROM employees e1,employees e2</span><br><span class="line">WHERE e1.last_name = &#x27;Abel&#x27;</span><br><span class="line">AND e1.`salary` &lt; e2.`salary`</span><br></pre></td></tr></table></figure>
<figure class="highlight plaintext"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line">#方式三：子查询</span><br><span class="line">SELECT last_name,salary</span><br><span class="line">FROM employees</span><br><span class="line">WHERE salary &gt; (</span><br><span class="line">		SELECT salary</span><br><span class="line">		FROM employees</span><br><span class="line">		WHERE last_name = &#x27;Abel&#x27;</span><br><span class="line">		);</span><br></pre></td></tr></table></figure>
<p> <img src= "" data-lazy-src="https://www.naste.top:9000/webp/1554991316599.webp" alt="1554991316599"></p>
<h3 id="1-2-子查询的基本使用"><a href="#1-2-子查询的基本使用" class="headerlink" title="1.2 子查询的基本使用"></a>1.2 子查询的基本使用</h3><ul>
<li><p>子查询的基本语法结构：</p>
<p><img src= "" data-lazy-src="https://www.naste.top:9000/webp/1554991054388.webp" alt="1554991054388"></p>
</li>
<li><p>子查询（内查询）在主查询之前一次执行完成。</p>
</li>
<li>子查询的结果被主查询（外查询）使用 。</li>
<li><strong>注意事项</strong><ul>
<li>子查询要包含在括号内</li>
<li>将子查询放在比较条件的右侧</li>
<li>单行操作符对应单行子查询，多行操作符对应多行子查询</li>
</ul>
</li>
</ul>
<h3 id="1-3-子查询的分类"><a href="#1-3-子查询的分类" class="headerlink" title="1.3 子查询的分类"></a>1.3 子查询的分类</h3><p><strong>分类方式1：</strong></p>
<p>我们按内查询的结果返回一条还是多条记录，将子查询分为<code>单行子查询</code>、<code>多行子查询</code>。</p>
<ul>
<li><p>单行子查询</p>
<p><img src= "" data-lazy-src="https://www.naste.top:9000/webp/1554991538719.webp" alt="1554991538719"></p>
</li>
<li><p>多行子查询</p>
</li>
</ul>
<p><img src= "" data-lazy-src="https://www.naste.top:9000/webp/1554991555669.webp" alt="1554991555669"></p>
<p><strong>分类方式2：</strong></p>
<p>我们按内查询是否被执行多次，将子查询划分为<code>相关(或关联)子查询</code>和<code>不相关(或非关联)子查询</code>。</p>
<p>子查询从数据表中查询了数据结果，如果这个数据结果只执行一次，然后这个数据结果作为主查询的条件进行执行，那么这样的子查询叫做不相关子查询。</p>
<p>同样，如果子查询需要执行多次，即采用循环的方式，先从外部查询开始，每次都传入子查询进行查询，然后再将结果反馈给外部，这种嵌套的执行方式就称为相关子查询。</p>
<h2 id="2-单行子查询"><a href="#2-单行子查询" class="headerlink" title="2. 单行子查询"></a>2. 单行子查询</h2><h3 id="2-1-单行比较操作符"><a href="#2-1-单行比较操作符" class="headerlink" title="2.1 单行比较操作符"></a>2.1 单行比较操作符</h3><div class="table-container">
<table>
<thead>
<tr>
<th>操作符</th>
<th>含义</th>
</tr>
</thead>
<tbody>
<tr>
<td>=</td>
<td>equal to</td>
</tr>
<tr>
<td>&gt;</td>
<td>greater than</td>
</tr>
<tr>
<td>&gt;=</td>
<td>greater than or equal to</td>
</tr>
<tr>
<td>&lt;</td>
<td>less than</td>
</tr>
<tr>
<td>&lt;=</td>
<td>less than or equal to</td>
</tr>
<tr>
<td>&lt;&gt;</td>
<td>not equal to</td>
</tr>
</tbody>
</table>
</div>
<h3 id="2-2-代码示例"><a href="#2-2-代码示例" class="headerlink" title="2.2 代码示例"></a>2.2 代码示例</h3><p><strong>题目：查询工资大于149号员工工资的员工的信息</strong></p>
<p> <img src= "" data-lazy-src="https://www.naste.top:9000/webp/image-20210914232952626.webp" alt="image-20210914232952626"></p>
<p> <img src= "" data-lazy-src="https://www.naste.top:9000/webp/image-20210914232935062.webp" alt="image-20210914232935062"></p>
<p><strong>题目：返回job_id与141号员工相同，salary比143号员工多的员工姓名，job_id和工资</strong></p>
<figure class="highlight sql"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">SELECT</span> last_name, job_id, salary</span><br><span class="line"><span class="keyword">FROM</span>   employees</span><br><span class="line"><span class="keyword">WHERE</span>  job_id <span class="operator">=</span>  </span><br><span class="line">                (<span class="keyword">SELECT</span> job_id</span><br><span class="line">                 <span class="keyword">FROM</span>   employees</span><br><span class="line">                 <span class="keyword">WHERE</span>  employee_id <span class="operator">=</span> <span class="number">141</span>)</span><br><span class="line"><span class="keyword">AND</span>    salary <span class="operator">&gt;</span></span><br><span class="line">                (<span class="keyword">SELECT</span> salary</span><br><span class="line">                 <span class="keyword">FROM</span>   employees</span><br><span class="line">                 <span class="keyword">WHERE</span>  employee_id <span class="operator">=</span> <span class="number">143</span>);</span><br></pre></td></tr></table></figure>
<p><img src= "" data-lazy-src="https://www.naste.top:9000/webp/1554991892770.webp" alt="1554991892770"></p>
<p><strong>题目：返回公司工资最少的员工的last_name,job_id和salary</strong></p>
<figure class="highlight sql"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">SELECT</span> last_name, job_id, salary</span><br><span class="line"><span class="keyword">FROM</span>   employees</span><br><span class="line"><span class="keyword">WHERE</span>  salary <span class="operator">=</span> </span><br><span class="line">                (<span class="keyword">SELECT</span> <span class="built_in">MIN</span>(salary)</span><br><span class="line">                 <span class="keyword">FROM</span>   employees);</span><br></pre></td></tr></table></figure>
<p><img src= "" data-lazy-src="https://www.naste.top:9000/webp/1554991935186.webp" alt="1554991935186"></p>
<p><strong>题目：查询与141号或174号员工的manager_id和department_id相同的其他员工的employee_id，manager_id，department_id</strong></p>
<p>实现方式1：不成对比较</p>
<figure class="highlight sas"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">SELECT</span>  employee_id, manager_id, department_id</span><br><span class="line"><span class="keyword">FROM</span>    employees</span><br><span class="line"><span class="keyword">WHERE</span>   manager_id <span class="keyword">IN</span></span><br><span class="line">		  (<span class="keyword">SELECT</span>  manager_id</span><br><span class="line">                   <span class="keyword">FROM</span>    employees</span><br><span class="line">                   <span class="keyword">WHERE</span>   employee_id <span class="keyword">IN</span> (174,141))</span><br><span class="line"><span class="keyword">AND</span>     department_id <span class="keyword">IN</span> </span><br><span class="line">		  (<span class="keyword">SELECT</span>  department_id</span><br><span class="line">                   <span class="keyword">FROM</span>    employees</span><br><span class="line">                   <span class="keyword">WHERE</span>   employee_id <span class="keyword">IN</span> (174,141))</span><br><span class="line"><span class="keyword">AND</span>	employee_id <span class="keyword">NOT</span> I<span class="meta">N</span>(174,141);</span><br></pre></td></tr></table></figure>
<p>实现方式2：成对比较</p>
<figure class="highlight n1ql"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">SELECT</span>	employee_id, manager_id, department_id</span><br><span class="line"><span class="keyword">FROM</span>	employees</span><br><span class="line"><span class="keyword">WHERE</span>  (manager_id, department_id) <span class="keyword">IN</span></span><br><span class="line">                      (<span class="keyword">SELECT</span> manager_id, department_id</span><br><span class="line">                       <span class="keyword">FROM</span>   employees</span><br><span class="line">                       <span class="keyword">WHERE</span>  employee_id <span class="keyword">IN</span> (<span class="number">141</span>,<span class="number">174</span>))</span><br><span class="line"><span class="keyword">AND</span>	employee_id <span class="keyword">NOT</span> <span class="keyword">IN</span> (<span class="number">141</span>,<span class="number">174</span>);</span><br></pre></td></tr></table></figure>
<h3 id="2-3-HAVING-中的子查询"><a href="#2-3-HAVING-中的子查询" class="headerlink" title="2.3 HAVING 中的子查询"></a>2.3 HAVING 中的子查询</h3><ul>
<li>首先执行子查询。</li>
<li>向主查询中的HAVING 子句返回结果。</li>
</ul>
<p><strong>题目：查询最低工资大于50号部门最低工资的部门id和其最低工资</strong></p>
<figure class="highlight sql"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">SELECT</span>   department_id, <span class="built_in">MIN</span>(salary)</span><br><span class="line"><span class="keyword">FROM</span>     employees</span><br><span class="line"><span class="keyword">GROUP</span> <span class="keyword">BY</span> department_id</span><br><span class="line"><span class="keyword">HAVING</span>   <span class="built_in">MIN</span>(salary) <span class="operator">&gt;</span></span><br><span class="line">                       (<span class="keyword">SELECT</span> <span class="built_in">MIN</span>(salary)</span><br><span class="line">                        <span class="keyword">FROM</span>   employees</span><br><span class="line">                        <span class="keyword">WHERE</span>  department_id <span class="operator">=</span> <span class="number">50</span>);</span><br></pre></td></tr></table></figure>
<h3 id="2-4-CASE中的子查询"><a href="#2-4-CASE中的子查询" class="headerlink" title="2.4 CASE中的子查询"></a>2.4 CASE中的子查询</h3><p>在CASE表达式中使用单列子查询：</p>
<p><strong>题目：显式员工的employee_id,last_name和location。其中，若员工department_id与location_id为1800的department_id相同，则location为’Canada’，其余则为’USA’。</strong></p>
<figure class="highlight pgsql"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">SELECT</span> employee_id, last_name,</span><br><span class="line">       (<span class="keyword">CASE</span> department_id</span><br><span class="line">        <span class="keyword">WHEN</span></span><br><span class="line">             (<span class="keyword">SELECT</span> department_id <span class="keyword">FROM</span> departments</span><br><span class="line">	      <span class="keyword">WHERE</span> location_id = <span class="number">1800</span>)           </span><br><span class="line">        <span class="keyword">THEN</span> <span class="string">&#x27;Canada&#x27;</span> <span class="keyword">ELSE</span> <span class="string">&#x27;USA&#x27;</span> <span class="keyword">END</span>) <span class="keyword">location</span></span><br><span class="line"><span class="keyword">FROM</span>   employees;</span><br></pre></td></tr></table></figure>
<h3 id="2-5-子查询中的空值问题"><a href="#2-5-子查询中的空值问题" class="headerlink" title="2.5 子查询中的空值问题"></a>2.5 子查询中的空值问题</h3><figure class="highlight sql"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">SELECT</span> last_name, job_id</span><br><span class="line"><span class="keyword">FROM</span>   employees</span><br><span class="line"><span class="keyword">WHERE</span>  job_id <span class="operator">=</span></span><br><span class="line">                (<span class="keyword">SELECT</span> job_id</span><br><span class="line">                 <span class="keyword">FROM</span>   employees</span><br><span class="line">                 <span class="keyword">WHERE</span>  last_name <span class="operator">=</span> <span class="string">&#x27;Haas&#x27;</span>);</span><br></pre></td></tr></table></figure>
<p><img src= "" data-lazy-src="https://www.naste.top:9000/webp/1554992067381.webp" alt="1554992067381"></p>
<blockquote>
<p><strong>子查询不返回任何行</strong></p>
</blockquote>
<h3 id="2-5-非法使用子查询"><a href="#2-5-非法使用子查询" class="headerlink" title="2.5 非法使用子查询"></a>2.5 非法使用子查询</h3><figure class="highlight sql"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">SELECT</span> employee_id, last_name</span><br><span class="line"><span class="keyword">FROM</span>   employees</span><br><span class="line"><span class="keyword">WHERE</span>  salary <span class="operator">=</span></span><br><span class="line">                (<span class="keyword">SELECT</span>   <span class="built_in">MIN</span>(salary)</span><br><span class="line">                 <span class="keyword">FROM</span>     employees</span><br><span class="line">                 <span class="keyword">GROUP</span> <span class="keyword">BY</span> department_id);</span><br></pre></td></tr></table></figure>
<p><img src= "" data-lazy-src="https://www.naste.top:9000/webp/1554992135819.webp" alt="1554992135819"></p>
<blockquote>
<p><strong>多行子查询使用单行比较符</strong></p>
</blockquote>
<h2 id="3-多行子查询"><a href="#3-多行子查询" class="headerlink" title="3. 多行子查询"></a>3. 多行子查询</h2><ul>
<li>也称为集合比较子查询</li>
<li>内查询返回多行</li>
<li>使用多行比较操作符</li>
</ul>
<h3 id="3-1-多行比较操作符"><a href="#3-1-多行比较操作符" class="headerlink" title="3.1 多行比较操作符"></a>3.1 多行比较操作符</h3><div class="table-container">
<table>
<thead>
<tr>
<th>操作符</th>
<th>含义</th>
</tr>
</thead>
<tbody>
<tr>
<td>IN</td>
<td>等于列表中的<strong>任意一个</strong></td>
</tr>
<tr>
<td>ANY</td>
<td>需要和单行比较操作符一起使用，和子查询返回的<strong>某一个</strong>值比较</td>
</tr>
<tr>
<td>ALL</td>
<td>需要和单行比较操作符一起使用，和子查询返回的<strong>所有</strong>值比较</td>
</tr>
<tr>
<td>SOME</td>
<td>实际上是ANY的别名，作用相同，一般常使用ANY</td>
</tr>
</tbody>
</table>
</div>
<blockquote>
<p>体会 ANY 和 ALL 的区别</p>
</blockquote>
<h3 id="3-2-代码示例"><a href="#3-2-代码示例" class="headerlink" title="3.2 代码示例"></a>3.2 代码示例</h3><p><strong>题目：返回其它job_id中比job_id为‘IT_PROG’部门任一工资低的员工的员工号、姓名、job_id 以及salary</strong></p>
<p><img src= "" data-lazy-src="https://www.naste.top:9000/webp/1554992658876.webp" alt="1554992658876"></p>
<p><img src= "" data-lazy-src="https://www.naste.top:9000/webp/1554992664594.webp" alt="1554992664594"></p>
<p><img src= "" data-lazy-src="https://www.naste.top:9000/webp/1554992668429.webp" alt="1554992668429"></p>
<p><strong>题目：返回其它job_id中比job_id为‘IT_PROG’部门所有工资都低的员工的员工号、姓名、job_id以及salary</strong></p>
<p><img src= "" data-lazy-src="https://www.naste.top:9000/webp/1554992753654.webp" alt="1554992753654"></p>
<p><img src= "" data-lazy-src="https://www.naste.top:9000/webp/1554992759467.webp" alt="1554992759467"></p>
<p><strong>题目：查询平均工资最低的部门id</strong></p>
<figure class="highlight plaintext"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br></pre></td><td class="code"><pre><span class="line">#方式1：</span><br><span class="line">SELECT department_id</span><br><span class="line">FROM employees</span><br><span class="line">GROUP BY department_id</span><br><span class="line">HAVING AVG(salary) = (</span><br><span class="line">			SELECT MIN(avg_sal)</span><br><span class="line">			FROM (</span><br><span class="line">				SELECT AVG(salary) avg_sal</span><br><span class="line">				FROM employees</span><br><span class="line">				GROUP BY department_id</span><br><span class="line">				) dept_avg_sal</span><br><span class="line">			)</span><br></pre></td></tr></table></figure>
<figure class="highlight plaintext"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line">#方式2：</span><br><span class="line">SELECT department_id</span><br><span class="line">FROM employees</span><br><span class="line">GROUP BY department_id</span><br><span class="line">HAVING AVG(salary) &lt;= ALL (</span><br><span class="line">				SELECT AVG(salary) avg_sal</span><br><span class="line">				FROM employees</span><br><span class="line">				GROUP BY department_id</span><br><span class="line">)</span><br></pre></td></tr></table></figure>
<h3 id="3-3-空值问题"><a href="#3-3-空值问题" class="headerlink" title="3.3 空值问题"></a>3.3 空值问题</h3><figure class="highlight plaintext"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line">SELECT last_name</span><br><span class="line">FROM employees</span><br><span class="line">WHERE employee_id NOT IN (</span><br><span class="line">			SELECT manager_id</span><br><span class="line">			FROM employees</span><br><span class="line">			);</span><br></pre></td></tr></table></figure>
<p> <img src= "" data-lazy-src="https://www.naste.top:9000/webp/image-20211027195906773.webp" alt="image-20211027195906773"></p>
<h2 id="4-相关子查询"><a href="#4-相关子查询" class="headerlink" title="4. 相关子查询"></a>4. 相关子查询</h2><h3 id="4-1-相关子查询执行流程"><a href="#4-1-相关子查询执行流程" class="headerlink" title="4.1 相关子查询执行流程"></a>4.1 相关子查询执行流程</h3><p>如果子查询的执行依赖于外部查询，通常情况下都是因为子查询中的表用到了外部的表，并进行了条件关联，因此每执行一次外部查询，子查询都要重新计算一次，这样的子查询就称之为<code>关联子查询</code>。</p>
<p>相关子查询按照一行接一行的顺序执行，主查询的每一行都执行一次子查询。</p>
<p><img src= "" data-lazy-src="https://www.naste.top:9000/webp/1554992898234.webp" alt="1554992898234" style="zoom:80%;" /></p>
<p><img src= "" data-lazy-src="https://www.naste.top:9000/webp/1554992925281.webp" alt="1554992925281" style="zoom:80%;" /></p>
<p>说明：<strong>子查询中使用主查询中的列</strong></p>
<h3 id="4-2-代码示例"><a href="#4-2-代码示例" class="headerlink" title="4.2 代码示例"></a>4.2 代码示例</h3><p><strong>题目：查询员工中工资大于本部门平均工资的员工的last_name,salary和其department_id</strong></p>
<p><strong>方式一：相关子查询</strong></p>
<p><img src= "" data-lazy-src="https://www.naste.top:9000/webp/1554992986225.webp" alt="1554992986225"></p>
<p><strong>方式二：在 FROM 中使用子查询</strong></p>
<figure class="highlight sql"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">SELECT</span> last_name,salary,e1.department_id</span><br><span class="line"><span class="keyword">FROM</span> employees e1,(<span class="keyword">SELECT</span> department_id,<span class="built_in">AVG</span>(salary) dept_avg_sal <span class="keyword">FROM</span> employees <span class="keyword">GROUP</span> <span class="keyword">BY</span> department_id) e2</span><br><span class="line"><span class="keyword">WHERE</span> e1.`department_id` <span class="operator">=</span> e2.department_id</span><br><span class="line"><span class="keyword">AND</span> e2.dept_avg_sal <span class="operator">&lt;</span> e1.`salary`;</span><br></pre></td></tr></table></figure>
<blockquote>
<p>from型的子查询：子查询是作为from的一部分，子查询要用()引起来，并且要给这个子查询取别名，<br>把它当成一张“临时的虚拟的表”来使用。</p>
</blockquote>
<p>在ORDER BY 中使用子查询：</p>
<p><strong>题目：查询员工的id,salary,按照department_name 排序</strong></p>
<figure class="highlight sql"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">SELECT</span> employee_id,salary</span><br><span class="line"><span class="keyword">FROM</span> employees e</span><br><span class="line"><span class="keyword">ORDER</span> <span class="keyword">BY</span> (</span><br><span class="line">	  <span class="keyword">SELECT</span> department_name</span><br><span class="line">	  <span class="keyword">FROM</span> departments d</span><br><span class="line">	  <span class="keyword">WHERE</span> e.`department_id` <span class="operator">=</span> d.`department_id`</span><br><span class="line">	);</span><br></pre></td></tr></table></figure>
<p><strong>题目：若employees表中employee_id与job_history表中employee_id相同的数目不小于2，输出这些相同id的员工的employee_id,last_name和其job_id</strong></p>
<figure class="highlight n1ql"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">SELECT</span> <span class="built_in">e</span>.employee_id, last_name,<span class="built_in">e</span>.job_id</span><br><span class="line"><span class="keyword">FROM</span>   employees <span class="built_in">e</span> </span><br><span class="line"><span class="keyword">WHERE</span>  <span class="number">2</span> &lt;= (<span class="keyword">SELECT</span> <span class="built_in">COUNT</span>(*)</span><br><span class="line">             <span class="keyword">FROM</span>   job_history </span><br><span class="line">             <span class="keyword">WHERE</span>  employee_id = <span class="built_in">e</span>.employee_id);</span><br></pre></td></tr></table></figure>
<h3 id="4-3-EXISTS-与-NOT-EXISTS关键字"><a href="#4-3-EXISTS-与-NOT-EXISTS关键字" class="headerlink" title="4.3 EXISTS 与 NOT EXISTS关键字"></a>4.3 EXISTS 与 NOT EXISTS关键字</h3><ul>
<li>关联子查询通常也会和 EXISTS操作符一起来使用，用来检查在子查询中是否存在满足条件的行。</li>
<li><strong>如果在子查询中不存在满足条件的行：</strong><ul>
<li>条件返回 FALSE</li>
<li>继续在子查询中查找</li>
</ul>
</li>
<li><strong>如果在子查询中存在满足条件的行：</strong><ul>
<li>不在子查询中继续查找</li>
<li>条件返回 TRUE</li>
</ul>
</li>
<li>NOT EXISTS关键字表示如果不存在某种条件，则返回TRUE，否则返回FALSE。</li>
</ul>
<p><strong>题目：查询公司管理者的employee_id，last_name，job_id，department_id信息</strong></p>
<p>方式一：</p>
<figure class="highlight sql"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">SELECT</span> employee_id, last_name, job_id, department_id</span><br><span class="line"><span class="keyword">FROM</span>   employees e1</span><br><span class="line"><span class="keyword">WHERE</span>  <span class="keyword">EXISTS</span> ( <span class="keyword">SELECT</span> <span class="operator">*</span></span><br><span class="line">                 <span class="keyword">FROM</span>   employees e2</span><br><span class="line">                 <span class="keyword">WHERE</span>  e2.manager_id <span class="operator">=</span> </span><br><span class="line">                        e1.employee_id);</span><br></pre></td></tr></table></figure>
<p>方式二：自连接</p>
<figure class="highlight sql"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">SELECT</span> <span class="keyword">DISTINCT</span> e1.employee_id, e1.last_name, e1.job_id, e1.department_id</span><br><span class="line"><span class="keyword">FROM</span>   employees e1 <span class="keyword">JOIN</span> employees e2</span><br><span class="line"><span class="keyword">WHERE</span> e1.employee_id <span class="operator">=</span> e2.manager_id;</span><br></pre></td></tr></table></figure>
<p>方式三：</p>
<figure class="highlight sql"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">SELECT</span> employee_id,last_name,job_id,department_id</span><br><span class="line"><span class="keyword">FROM</span> employees</span><br><span class="line"><span class="keyword">WHERE</span> employee_id <span class="keyword">IN</span> (</span><br><span class="line">		     <span class="keyword">SELECT</span> <span class="keyword">DISTINCT</span> manager_id</span><br><span class="line">		     <span class="keyword">FROM</span> employees</span><br><span class="line">		     </span><br><span class="line">		     );</span><br></pre></td></tr></table></figure>
<p><strong>题目：查询departments表中，不存在于employees表中的部门的department_id和department_name</strong></p>
<figure class="highlight sql"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">SELECT</span> department_id, department_name</span><br><span class="line"><span class="keyword">FROM</span> departments d</span><br><span class="line"><span class="keyword">WHERE</span> <span class="keyword">NOT</span> <span class="keyword">EXISTS</span> (<span class="keyword">SELECT</span> <span class="string">&#x27;X&#x27;</span></span><br><span class="line">                  <span class="keyword">FROM</span>   employees</span><br><span class="line">                  <span class="keyword">WHERE</span>  department_id <span class="operator">=</span> d.department_id);</span><br></pre></td></tr></table></figure>
<p><img src= "" data-lazy-src="https://www.naste.top:9000/webp/1554993169269.webp" alt="1554993169269"></p>
<h3 id="4-4-相关更新"><a href="#4-4-相关更新" class="headerlink" title="4.4 相关更新"></a>4.4 相关更新</h3><figure class="highlight sql"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">UPDATE</span> table1 alias1</span><br><span class="line"><span class="keyword">SET</span>    <span class="keyword">column</span> <span class="operator">=</span> (<span class="keyword">SELECT</span> expression</span><br><span class="line">                 <span class="keyword">FROM</span>   table2 alias2</span><br><span class="line">                 <span class="keyword">WHERE</span>  alias1.column <span class="operator">=</span> alias2.column);</span><br></pre></td></tr></table></figure>
<p>使用相关子查询依据一个表中的数据更新另一个表的数据。</p>
<p><strong>题目：在employees中增加一个department_name字段，数据为员工对应的部门名称</strong></p>
<figure class="highlight plaintext"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line"># 1）</span><br><span class="line">ALTER TABLE employees</span><br><span class="line">ADD(department_name VARCHAR2(14));</span><br><span class="line"></span><br><span class="line"># 2）</span><br><span class="line">UPDATE employees e</span><br><span class="line">SET department_name =  (SELECT department_name </span><br><span class="line">	                       FROM   departments d</span><br><span class="line">	                       WHERE  e.department_id = d.department_id);</span><br><span class="line"></span><br></pre></td></tr></table></figure>
<h3 id="4-4-相关删除"><a href="#4-4-相关删除" class="headerlink" title="4.4 相关删除"></a>4.4 相关删除</h3><figure class="highlight sql"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">DELETE</span> <span class="keyword">FROM</span> table1 alias1</span><br><span class="line"><span class="keyword">WHERE</span> <span class="keyword">column</span> operator (<span class="keyword">SELECT</span> expression</span><br><span class="line">                       <span class="keyword">FROM</span>   table2 alias2</span><br><span class="line">                       <span class="keyword">WHERE</span>  alias1.column <span class="operator">=</span> alias2.column);</span><br></pre></td></tr></table></figure>
<p>使用相关子查询依据一个表中的数据删除另一个表的数据。</p>
<p><strong>题目：删除表employees中，其与emp_history表皆有的数据</strong></p>
<figure class="highlight sql"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">DELETE</span> <span class="keyword">FROM</span> employees e</span><br><span class="line"><span class="keyword">WHERE</span> employee_id <span class="keyword">in</span>  </span><br><span class="line">           (<span class="keyword">SELECT</span> employee_id</span><br><span class="line">            <span class="keyword">FROM</span>   emp_history </span><br><span class="line">            <span class="keyword">WHERE</span>  employee_id <span class="operator">=</span> e.employee_id);</span><br></pre></td></tr></table></figure>
<h2 id="5-抛一个思考题"><a href="#5-抛一个思考题" class="headerlink" title="5. 抛一个思考题"></a>5. 抛一个思考题</h2><p><strong>问题：</strong>谁的工资比Abel的高？</p>
<p><strong>解答：</strong></p>
<figure class="highlight plaintext"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line">#方式1：自连接</span><br><span class="line">SELECT e2.last_name,e2.salary</span><br><span class="line">FROM employees e1,employees e2</span><br><span class="line">WHERE e1.last_name = &#x27;Abel&#x27;</span><br><span class="line">AND e1.`salary` &lt; e2.`salary`</span><br></pre></td></tr></table></figure>
<figure class="highlight plaintext"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line">#方式2：子查询</span><br><span class="line">SELECT last_name,salary</span><br><span class="line">FROM employees</span><br><span class="line">WHERE salary &gt; (</span><br><span class="line">		SELECT salary</span><br><span class="line">		FROM employees</span><br><span class="line">		WHERE last_name = &#x27;Abel&#x27;</span><br><span class="line">		);</span><br></pre></td></tr></table></figure>
<p><strong>问题：</strong>以上两种方式有好坏之分吗？</p>
<p><strong>解答：</strong>自连接方式好！</p>
<p>题目中可以使用子查询，也可以使用自连接。一般情况建议你使用自连接，因为在许多 DBMS 的处理过程中，对于自连接的处理速度要比子查询快得多。</p>
<p>可以这样理解：子查询实际上是通过未知表进行查询后的条件判断，而自连接是通过已知的自身数据表进行条件判断，因此在大部分 DBMS 中都对自连接处理进行了优化。</p>
</article><div class="post-copyright"><div class="post-copyright__title"><span class="post-copyright-info"><h>第九-MySQL子查询</h></span></div><div class="post-copyright__type"><span class="post-copyright-info"><a href="https://www.naste.top:1024/posts/2896002004.html">https://www.naste.top:1024/posts/2896002004.html</a></span></div><div class="post-copyright-m"><div class="post-copyright-m-info"><div class="post-copyright-a"><h>作者</h><div class="post-copyright-cc-info"><h>XiaoFei🥝</h></div></div><div class="post-copyright-c"><h>发布于</h><div class="post-copyright-cc-info"><h>2022-09-19</h></div></div><div class="post-copyright-u"><h>更新于</h><div class="post-copyright-cc-info"><h>2024-04-26</h></div></div><div class="post-copyright-c"><h>许可协议</h><div class="post-copyright-cc-info"><a class="icon" rel="noopener" target="_blank" title="Creative Commons" href="https://creativecommons.org/"><i class="fab fa-creative-commons"></i></a><a rel="noopener" target="_blank" title="CC BY-NC-SA 4.0" 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class="toc"><li class="toc-item toc-level-1"><a class="toc-link" href="#%E7%AC%AC09%E7%AB%A0-%E5%AD%90%E6%9F%A5%E8%AF%A2"><span class="toc-text">第09章_子查询</span></a><ol class="toc-child"><li class="toc-item toc-level-2"><a class="toc-link" href="#1-%E9%9C%80%E6%B1%82%E5%88%86%E6%9E%90%E4%B8%8E%E9%97%AE%E9%A2%98%E8%A7%A3%E5%86%B3"><span class="toc-text">1. 需求分析与问题解决</span></a><ol class="toc-child"><li class="toc-item toc-level-3"><a class="toc-link" href="#1-1-%E5%AE%9E%E9%99%85%E9%97%AE%E9%A2%98"><span class="toc-text">1.1 实际问题</span></a></li><li class="toc-item toc-level-3"><a class="toc-link" href="#1-2-%E5%AD%90%E6%9F%A5%E8%AF%A2%E7%9A%84%E5%9F%BA%E6%9C%AC%E4%BD%BF%E7%94%A8"><span class="toc-text">1.2 子查询的基本使用</span></a></li><li class="toc-item toc-level-3"><a class="toc-link" href="#1-3-%E5%AD%90%E6%9F%A5%E8%AF%A2%E7%9A%84%E5%88%86%E7%B1%BB"><span class="toc-text">1.3 子查询的分类</span></a></li></ol></li><li class="toc-item toc-level-2"><a class="toc-link" href="#2-%E5%8D%95%E8%A1%8C%E5%AD%90%E6%9F%A5%E8%AF%A2"><span class="toc-text">2. 单行子查询</span></a><ol class="toc-child"><li class="toc-item toc-level-3"><a class="toc-link" href="#2-1-%E5%8D%95%E8%A1%8C%E6%AF%94%E8%BE%83%E6%93%8D%E4%BD%9C%E7%AC%A6"><span class="toc-text">2.1 单行比较操作符</span></a></li><li class="toc-item toc-level-3"><a class="toc-link" href="#2-2-%E4%BB%A3%E7%A0%81%E7%A4%BA%E4%BE%8B"><span class="toc-text">2.2 代码示例</span></a></li><li class="toc-item toc-level-3"><a class="toc-link" href="#2-3-HAVING-%E4%B8%AD%E7%9A%84%E5%AD%90%E6%9F%A5%E8%AF%A2"><span class="toc-text">2.3 HAVING 中的子查询</span></a></li><li class="toc-item toc-level-3"><a class="toc-link" href="#2-4-CASE%E4%B8%AD%E7%9A%84%E5%AD%90%E6%9F%A5%E8%AF%A2"><span class="toc-text">2.4 CASE中的子查询</span></a></li><li class="toc-item toc-level-3"><a class="toc-link" href="#2-5-%E5%AD%90%E6%9F%A5%E8%AF%A2%E4%B8%AD%E7%9A%84%E7%A9%BA%E5%80%BC%E9%97%AE%E9%A2%98"><span class="toc-text">2.5 子查询中的空值问题</span></a></li><li class="toc-item toc-level-3"><a class="toc-link" href="#2-5-%E9%9D%9E%E6%B3%95%E4%BD%BF%E7%94%A8%E5%AD%90%E6%9F%A5%E8%AF%A2"><span class="toc-text">2.5 非法使用子查询</span></a></li></ol></li><li class="toc-item toc-level-2"><a class="toc-link" href="#3-%E5%A4%9A%E8%A1%8C%E5%AD%90%E6%9F%A5%E8%AF%A2"><span class="toc-text">3. 多行子查询</span></a><ol class="toc-child"><li class="toc-item toc-level-3"><a class="toc-link" href="#3-1-%E5%A4%9A%E8%A1%8C%E6%AF%94%E8%BE%83%E6%93%8D%E4%BD%9C%E7%AC%A6"><span class="toc-text">3.1 多行比较操作符</span></a></li><li class="toc-item toc-level-3"><a class="toc-link" href="#3-2-%E4%BB%A3%E7%A0%81%E7%A4%BA%E4%BE%8B"><span class="toc-text">3.2 代码示例</span></a></li><li class="toc-item toc-level-3"><a class="toc-link" href="#3-3-%E7%A9%BA%E5%80%BC%E9%97%AE%E9%A2%98"><span class="toc-text">3.3 空值问题</span></a></li></ol></li><li class="toc-item toc-level-2"><a class="toc-link" href="#4-%E7%9B%B8%E5%85%B3%E5%AD%90%E6%9F%A5%E8%AF%A2"><span class="toc-text">4. 相关子查询</span></a><ol class="toc-child"><li class="toc-item toc-level-3"><a class="toc-link" href="#4-1-%E7%9B%B8%E5%85%B3%E5%AD%90%E6%9F%A5%E8%AF%A2%E6%89%A7%E8%A1%8C%E6%B5%81%E7%A8%8B"><span class="toc-text">4.1 相关子查询执行流程</span></a></li><li class="toc-item toc-level-3"><a class="toc-link" href="#4-2-%E4%BB%A3%E7%A0%81%E7%A4%BA%E4%BE%8B"><span class="toc-text">4.2 代码示例</span></a></li><li class="toc-item toc-level-3"><a class="toc-link" href="#4-3-EXISTS-%E4%B8%8E-NOT-EXISTS%E5%85%B3%E9%94%AE%E5%AD%97"><span class="toc-text">4.3 EXISTS 与 NOT EXISTS关键字</span></a></li><li class="toc-item toc-level-3"><a class="toc-link" href="#4-4-%E7%9B%B8%E5%85%B3%E6%9B%B4%E6%96%B0"><span class="toc-text">4.4 相关更新</span></a></li><li class="toc-item toc-level-3"><a class="toc-link" href="#4-4-%E7%9B%B8%E5%85%B3%E5%88%A0%E9%99%A4"><span class="toc-text">4.4 相关删除</span></a></li></ol></li><li class="toc-item toc-level-2"><a class="toc-link" href="#5-%E6%8A%9B%E4%B8%80%E4%B8%AA%E6%80%9D%E8%80%83%E9%A2%98"><span 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    var item_html = '<div class="recent-post-item" style="height: auto;width: 100%"><div class="blog-slider swiper-container-fade swiper-container-horizontal" id="swiper_container"><div class="blog-slider__wrp swiper-wrapper" style="transition-duration: 0ms;"><div class="blog-slider__item swiper-slide" style="width: 750px; opacity: 1; transform: translate3d(0px, 0px, 0px); transition-duration: 0ms;"><a class="blog-slider__img" onclick="pjax.loadUrl(&quot;posts/204253054.html&quot;);" href="javascript:void(0);" alt=""><img width="48" height="48" src= "" data-lazy-src="https://www.naste.top:9000/webp/1675912191.webp" alt="" onerror="this.src=https://unpkg.zhimg.com/akilar-candyassets/image/loading.gif; this.onerror = null;"/></a><div class="blog-slider__content"><span class="blog-slider__code">2023-03-08</span><a class="blog-slider__title" onclick="pjax.loadUrl(&quot;posts/204253054.html&quot;);" href="javascript:void(0);" alt="">SpringBoot使用实现定时任务和xxl-job实现分布式任务调度</a><div class="blog-slider__text">SpringBoot使用实现定时任务和xxl-job实现分布式任务调度</div><a class="blog-slider__button" onclick="pjax.loadUrl(&quot;posts/204253054.html&quot;);" href="javascript:void(0);" alt="">详情       </a></div></div><div class="blog-slider__item swiper-slide" style="width: 750px; opacity: 1; transform: translate3d(0px, 0px, 0px); transition-duration: 0ms;"><a class="blog-slider__img" onclick="pjax.loadUrl(&quot;posts/538133837.html&quot;);" href="javascript:void(0);" alt=""><img width="48" height="48" src= "" data-lazy-src="https://www.naste.top:9000/webp/1678672933.webp" alt="" onerror="this.src=https://unpkg.zhimg.com/akilar-candyassets/image/loading.gif; this.onerror = null;"/></a><div class="blog-slider__content"><span class="blog-slider__code">2023-03-15</span><a class="blog-slider__title" onclick="pjax.loadUrl(&quot;posts/538133837.html&quot;);" href="javascript:void(0);" alt="">Hexo中Markdown语法与外挂标签写法汇总</a><div class="blog-slider__text">Hexo中Markdown语法与外挂标签写法汇总</div><a class="blog-slider__button" onclick="pjax.loadUrl(&quot;posts/538133837.html&quot;);" href="javascript:void(0);" alt="">详情       </a></div></div></div><div class="blog-slider__pagination swiper-pagination-clickable swiper-pagination-bullets"></div></div></div>';
    console.log('已挂载butterfly_swiper')
    parent_div_git.insertAdjacentHTML("afterbegin",item_html)
    }
  var elist = 'undefined'.split(',');
  var cpage = location.pathname;
  var epage = '/';
  var flag = 0;

  for (var i=0;i<elist.length;i++){
    if (cpage.includes(elist[i])){
      flag++;
    }
  }

  if ((epage ==='all')&&(flag == 0)){
    butterfly_swiper_injector_config();
  }
  else if (epage === cpage){
    butterfly_swiper_injector_config();
  }
  </script><script defer src="https://npm.elemecdn.com/hexo-butterfly-swiper/lib/swiper.min.js"></script><script defer data-pjax src="https://npm.elemecdn.com/hexo-butterfly-swiper/lib/swiper_init.js"></script><div class="js-pjax"><script async="async">var arr = document.getElementsByClassName('recent-post-item');
for(var i = 0;i<arr.length;i++){
    arr[i].classList.add('wow');
    arr[i].classList.add('animate__zoomIn');
    arr[i].setAttribute('data-wow-duration', '2s');
    arr[i].setAttribute('data-wow-delay', '200ms');
    arr[i].setAttribute('data-wow-offset', '30');
    arr[i].setAttribute('data-wow-iteration', '1');
  }</script><script async="async">var arr = document.getElementsByClassName('card-widget');
for(var i = 0;i<arr.length;i++){
    arr[i].classList.add('wow');
    arr[i].classList.add('animate__zoomIn');
    arr[i].setAttribute('data-wow-duration', '2s');
    arr[i].setAttribute('data-wow-delay', '200ms');
    arr[i].setAttribute('data-wow-offset', '30');
    arr[i].setAttribute('data-wow-iteration', '1');
  }</script></div><script defer src="https://npm.elemecdn.com/hexo-butterfly-wowjs/lib/wow.min.js"></script><script defer src="https://npm.elemecdn.com/hexo-butterfly-wowjs/lib/wow_init.js"></script><script data-pjax src="https://npm.elemecdn.com/hexo-filter-gitcalendar/lib/gitcalendar.js"></script><script data-pjax>
  function gitcalendar_injector_config(){
      var parent_div_git = document.getElementById('gitZone');
      var item_html = '<div class="recent-post-item" id="gitcalendarBar" style="width:100%;height:auto;padding:10px;"><style>#git_container{min-height: 320px}@media screen and (max-width:650px) {#git_container{min-height: 0px}}</style><div id="git_loading" style="width:10%;height:100%;margin:0 auto;display: block;"><svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 0 50 50" style="enable-background:new 0 0 50 50" xml:space="preserve"><path fill="#d0d0d0" d="M25.251,6.461c-10.318,0-18.683,8.365-18.683,18.683h4.068c0-8.071,6.543-14.615,14.615-14.615V6.461z" transform="rotate(275.098 25 25)"><animatetransform attributeType="xml" attributeName="transform" type="rotate" from="0 25 25" to="360 25 25" dur="0.6s" repeatCount="indefinite"></animatetransform></path></svg><style>#git_container{display: none;}</style></div><div id="git_container"></div></div>';
      parent_div_git.insertAdjacentHTML("afterbegin",item_html)
      console.log('已挂载gitcalendar')
      }

    if( document.getElementById('gitZone') && (location.pathname ==='/personal/about/'|| '/personal/about/' ==='all')){
        gitcalendar_injector_config()
        GitCalendarInit("https://gitcalendar.naste.top/api?xiao-i-fei",['#d9e0df', '#c6e0dc', '#a8dcd4', '#9adcd2', '#89ded1', '#77e0d0', '#5fdecb', '#47dcc6', '#39dcc3', '#1fdabe', '#00dab9'],'xiao-i-fei')
    }
  </script><!-- hexo injector body_end end --></body></html>